function Map(el) {
    this.el = el
    this.width = 800
    this.height = 400

}
Map.prototype.create = function () {
    // 设置div宽度高度背景边框
    // this代表map构造函数的实例
    this.el.style.width = this.width + 'px'
    this.el.style.height = this.height + 'px'
    this.el.style.background = 'url(./bg.png)'
    this.el.style.border = '12px solid green'
}